In bending pipe, and particularly larger diameter pipe from 6 inch diameter and larger, it is often beneficial or necessary to support the inner wall of the pipe near the bend. If unsupported, the bending forces exerted on the exterior of the pipe can cause severe deformation of the cross section of the pipe, reducing its strength and carrying capacity. It is particularly helpful to support the inner wall of the pipe in the portion which becomes the inside of the bend to prevent wrinkling of the pipe in this area.
In the past, large and complex internal mandrel devices have been employed. Such devices include the devices disclosed and illustrated in U.S. Pat. Nos. 3,834,210 and 3,851,519. These prior devices are typically provided with a plurality of metal shoes or strips which are expanded into contact with the inner walls of the pipe by a plurality of hydraulic cylinders. While these devices are effective, the complexity of the devices increase cost and maintenance requirements.
A need exists for an internal mandrel overcoming the disadvantages of the prior devices. The improved mandrel should have a minimum of operating components and operate with a minimum number of controls. The improved mandrel should be relatively lightweight and easy to move through the interior of the pipe prior to and after bending.